Preheat an outdoor grill for medium-high heat and lightly oil the grate. Rub a generous amount of salt over each steak. Spread a thick layer of mustard on each side of each steak. Sprinkle tea leaves over each steak until mustard is completely covered. Cook the steaks on the preheated grill until desired degree of doneness is reached, 5 to 10 minutes per side. An instant-read thermometer inserted into the center should read 140 degrees F (60 degrees C).